A consequence of ionizing radiation injury to normal tissue is production of a tumor bed effect (TBE) defined by altered growth of neoplasms in the damaged environment. Mechanistically, the TBE is thought to be a consequence of the inability of radiation-damaged vasculature to meet the demands of an expanding neoplastic population, and infers that tumor cells must compete for limited resources in a more hostile, stressful environment. We propose that this change in the micro-environment leads to an alteration of expression of growth factors involved in tumor-directed angiogenesis: specifically TGF-a and TGF-b. To test this hypothesis, we will use a battery of 9 human colon tumor cells, which show different levels of expression of, or response to, the polypeptide growth factors TGF-a and TGF-b. Solid xenograft tumors will be grown in nude mice and in either unirradiated or irradiated (20 Gy, 250 kVp x-rays) normal tissue. Levels of TGF-a and TGF-b mRNA as well as possible gene amplification will be assayed in sol id tumors as a function of tumor size using Northern and Southern blot techniques. These levels will be compared to levels of these cell lines growing in vitro. As these growth factors may act in both autocrine and paracrine fashion, we will also assay the numbers of receptors on these 9 human colon tumor lines in vitro using 125 I-labeled TGF-a and TGF-b. To quantitate the actual production of TGF-a and TGF-b, bioassay techniques will be used with these cell lines growing in vitro (specifically stimulation of NRK fibroblast growth and production of gel contraction in human foreskin fibroblast-loaded collagen gels). The results from these studies will be correlated with in vivo levels of TBE expression determined with volumetric techniques; with the extent of intratumoral hypoxia, with the numbers of host cells in tumors, and with flow cytometric data. With this information, we should be able to gain clinically relevant information on autocrine/paracrine regulation of neoplastic growth in normal or damaged microenvironments. Such data may then provide insight into why recurrent tumors are clinically more refractory to retreatment. If growth factor levels are increased, this may provide a relatively specific "target" for therapy (i.e.,by use of a blocking antibody which might be radioactively labeled).